Screw propeller



April 22, 1924.

- C. PINKERT SCREW PROPELLER Filed July 19. 1922 2 Sheets-Sheet 1 April 22 1924. 1,491,493

c. PINKERT 1 SCREW PROPELLER Filed July 19. 1922 2 Sheets-Sheet 2 Patented Apr. 22, i924.

PATENT OFFICE.

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SCREW PROPELLER.

Application filed July 19, 1922.

In air and water propellers the theoretically correct clean screw surface loses a considerable amount of its efiiciency as a result of incidental influences. Attempts have been made to remedy this by reducing the II pitch from the hub as the circumference is approached, but fully satisfactory results have not yet been obtained. The invention is based upon the recognition of the fact that. apart from the various large circumferential ways on' the various radii the varying great circumferential velocities per taining to same must be taken into consideration, so that despite the difference of these velocities a discharge of water, as uniform as possible, takes place from the point to the hub. For this purpose accordin to the invention the itches are so reduce as the circumference is ap roached, that in the vicinity of the circum erence the parts of the blade which there move more quickly against the water have lower pitches, not only in accordance to the greater distance covered but also in accordance to the greater shock when striking the water, due to the higher speed, whereas as the hub is approached the opposite conditions prevail for the same reason. As a practical measure for properly determining the pitch in this case the division of the radius of the propeller into an uneven number of parts, preferably five, is expedient, whereby the circumference of the hub lies on the innermost fifth of same and the middle pitch on the third fifth. 1

The amount of pitch reduction is an essential art of the invention, as explained below rom a number of examples.

The drawing shows a plan of the new propeller, whereby several applications are considered.

Fig. 1 is a circular diagram showing the fundamental circles for setting in the various pitches and the blade forms.

Figs. 2 to 5 are pitch diagrams from which Serial No. 576,109.

the essential kinds of pitch-increase as the hub is approached will be readily seen.

Fig. 6 is the diagram of a water passage to a propeller according to Fig. 5.

The radius is divided into five parts in such manner that five circumferential circles, 1, 2, 3, 4, 5, Fig. 1 at equal distances from each other are produced. The inside circle 1 is at the same time the hub circumference.

According to the first application (Fig. 2) the pitch 5, the lowest on the circumference, has been taken as base and the further pitches 8, s s 8 have in each event been enlarged a fifth of the pitch 3 According to'the second application (Fig. 3) the middle pitch 8 has been taken as base and from here, as the circumference is approached the pitches s and s have each time been reduced a fifth and as the hub is approached, the pitches s and 8 each increased a fifth.

According to the third application (Fig. 4) the point of departure has in turn been taken from the smallest pitch on the circumference in such manner that the next pitch 8 is a fifth larger than 8 the next pitch 8 also another fifth larger than a and so on.

According to the fourth application (Fig. 5) the middle pitch 8 on the third circle has been taken as point of departure. The formulas for the entire series of pitches on the five radii are as follows:

Pitch 8 :8 :0.6 Pitch 8 :8 :0.8 Pitch 8 8 211) Pitch 8 :8 :12 Pitch 8 8 :1.4;

The hub pitch is accordingly in this increase of pitches which is similar to a tangent curve more than double the pitch at the circumference.

This calculation is based on the following:

Figure 6 shows in simplified diagram form the water passage through the propeller blades. The relative movement of the liquid with respect to the screw takes place for each blade element on the radius 7, r, r and in corresponding planes which may be imagined as placed one over the other. The liquid which approaches the screw axially with the velocity at an endless distance from the screw, undergoes, in passing through, a change of velocity as well as of direction from (1 ac to ac, ae etc. In this way from 1, 2, 3, etc. circumferential velocity of the respective screw element is developed at the same time in a plane perpendicular to the axle. The lines e 6 e 6 etc. show the velocity of the water dischar e with respect to the screwbearer. The figure shows plainly how these are set in the same direction, Whereas in the case of non-varying pitch the directions diverge considerably.

On the assumption that the relative discharge velocities with respect to the screwbearer are'set in the same direction and become equally high, the following law must .be valid, which can also be deduced readily If in a model propeller @2100 mm. per second and one revolution, and 2,:1'00 as well, the constant i; and the total pitches become as follows:

A large number oftests showed, however, that this purely theoretical consideration, without taking into count the resistances met at the time, does not give satisfactory results, but that on the contrary a contorsion of the curve around. its center must take place in a certain sense, in order to overcome the resistance which appears in particular at the end of the hub. As the oontorsion on the hub-stem of the curve must be greater, in order to turn aside the i blades with a pitch decreasing velocity of the water discharge toward the middle more than at the end, the. final law of pitch may be best expressed as follows:

Pitch 8 :8 :0.5

8 :8 :LOG

found to be as follows:

The circular screw surface is according to Fig. 1 subdivided for this purpose, that is the sharp definition of the propeller outline by 10 concentric circles of the same annular width. Circle 1 is the nominal circle. In like manner radii are drawn symmetrically to center 2 at an angle of to the middle of the blade and the sixths of the surface of the circles are divided up in 8 similar parts=7.5 circular measure.

The projected surface of each screw propeller is now determined as follows:

1. Entering and emerging edges form a radius in running toward the hub 2. The outline is further determined by the points where the centric circles cross the radii. Compare surface I and surfaces II and III for twin screw steamers and the surfaces IV and V for single screw steamers, the surface outlines of which, however, may be varied still more in the same sense.

3. According to the charge and use of the propeller, as twin or single screw steamer, the entire surface within the third section of circle is divided u Havin n'owmorefiilly described and ascertaine the nature of my invention and in what manner the same is to be performed, I declare that what I claim is:

1. Screw propeller comprisin a hub and m the hub to the periphery, the largest radius being divided in equally stepped radii, a main pitch being provided on a certain radius on the other radii lying towards the hub the pitches each being enlarged successivel by the quotient of the main pitch divided by their number of radii.

2. Screw propeller comprising a hub and blades with a I itch decreasing from the hub to the perip ery, the largest radius being divided in equally stepped radii, a main pitch being provided on a certain radius, on the other radii lying towards the periphe'rythe pitches each being .descreased successively by the quotient of the main pitch divided by the number of radii.

3. Screw propeller comprising a hub and blades with a pitch descreasing from the hub to the periphery, the largest radius being divided in equally stepped radii, a main pitch being provided on a certain radius, on the other radii l ing'towards the hub every pitch being e arged b5 the quotient of theforegoing pitch ivide by the number of radii.

4. Screw propeller comprising hub and blades with a itch decreasing from the hub to the perip e the lar est radius being divided in equa y steppe radii, a main pitch being provided on a certain radius, on the other radii every successive pitch being as great as the quotient of the roduct of the inain pitch and number of re ii divided by numbers successively decreasing by one unit towards the hub.

5. Screw propeller comprising a hub and blades with a itch decreasing from the hub to the perip ery, the lar st radius being divided in equall steppe radii, a main pitch being provide on radius near to the middle of the length of the blade, on the other radii every successive pitch heir? essentially as great as the quotient o the product of the main pitch and number of radii divided by a number, which on the main pitch radius is equal to the number of radii, whilst it decreases towards the hub successively by one unit, and is enlarged towards the periphery successively by one unit.

6. Screw propeller comprisin a hub and blades with a pitch decreasing cm the hub to the periphery, (in accordance with claim 5), the anal view of the blade being substantially confined u to the middle of the length of the blade y radial edges up. to the maximum blade width, Whilst in the external part the blade is confined by spiral edge lines, drawn through the crossing points of equally distributed radii and equally distributed peripheral circles.

In witness whereof I affix my si ature.

CURT PINK RT. 

